Save plot with a given aspect ratio

Question

I'm working with the really awesome library ggplot2. I figured out how to set the aspect ratio of a plot by using coord_fixed. Now, I'd like to save the plot to a PDF with a specified width (e.g 10 cm) and let required height get calculated. I did not figure out how to achieve this. Is this even possible?

Answer 1

You can use grid functions to calculate the full size of the ggplot grob, but there are (edit: at least) two caveats:

• an extra device window will open, to do the unit conversion

• the plot panel size will be 0 by default, as it is meant to be calculated on-the-fly according to the device (viewport) it lives in, not the opposite.

That being said, the following function attempts to open a device that fits the ggplot exactly,

library(ggplot2) library(grid)  sizeit <- function(p, panel.size = 2, default.ar=1){    gb <- ggplot_build(p)   # first check if theme sets an aspect ratio   ar <- gb$plot$coordinates$ratio    # second possibility: aspect ratio is set by the coordinates, which results in    # the use of 'null' units for the gtable layout. let's find out   g <- ggplot_gtable(gb)   nullw <- sapply(g$widths, attr, "unit")   nullh <- sapply(g$heights, attr, "unit")    # ugly hack to extract the aspect ratio from these weird units   if(any(nullw == "null"))     ar <- unlist(g$widths[nullw == "null"]) / unlist(g$heights[nullh == "null"])    if(is.null(ar)) # if the aspect ratio wasn't specified by the plot        ar <- default.ar    # ensure that panel.size is always the larger dimension   if(ar <= 1 ) panel.size <- panel.size / ar    g$fullwidth <- convertWidth(sum(g$widths), "in", valueOnly=TRUE) +      panel.size   g$fullheight <- convertHeight(sum(g$heights), "in", valueOnly=TRUE) +      panel.size / ar    class(g) <- c("sizedgrob", class(g))   g }   print.sizedgrob <- function(x){   # note: dev.new doesn't seem to respect those parameters   # when called from Rstudio; in this case it    # may be replaced by x11 or quartz or ...   dev.new(width=x$fullwidth, height=x$fullheight)   grid.draw(x) }   p1 <- ggplot(mtcars, aes(x = wt, y = mpg)) + geom_point() + coord_fixed() +   theme(plot.background = element_rect(colour = "red"))  p2 <- p1 + aes(x = mpg, y = wt)  # need for an explicit dummy device open, otherwise it's a bit off # for no apparent reason that I can understand dev.new()   sizeit(p1, 0.1) 

sizeit(p2, 2)